1. Field of the Invention
This invention relates generally to diagnostic tests to determine the activity of serum cholinesterase. More particularly, the invention concerns a dry element and a method for determining serum cholinesterase activity in undiluted aqueous liquids.
2. Description of Related Art
The determination of the activity of serum cholinesterase (CHE) is important in the early diagnosis of various disease states such as degenerative liver disorders and poisoning caused by toxic agents such as insecticides and herbicides containing carbamates or organic phosphoric acid esters. These compounds inhibit CHE, thus a reduced level of CHE activity in a patient's serum might be diagnostic of chemical poisoning. In the case of carbamate pesticides, the inhibitory effect of these toxic agents might be reversed and cholinesterase activity restored if, for example, the patient's serum is diluted and the concentration of the toxic agent in the test reagent is lowered. In such cases, in vitro measurement of CHE activity in diluted samples might not truly reflect the severity of the in vivo state.
In determining the activity of CHE in serum it is customary to predilute the test serum sample because the level of CHE activity normally present in human sera is very high. Because such dilution could reverse CHE inhibition by toxic agents, it would be preferred to employ a method that is capable of determining a range of CHE activity without prior dilution of the test samples. One such method has been disclosed by Thomsen, Kewitz and Pleul, J. Clin. Chem. Clin. Biochem, vol.26/No.7, p.469-475 (1988). That method, however, employs a manual technique that uses reagents in wet solution and is therefore not as convenient or reproducible as automated methods or methods using dry analytical elements. Further, the reagents include radioactive labelled acetylcholine and thereby present certain known hazards.
It would be desirable to have a dry, analytical element for determining serum cholinesterase activity in undiluted aqueous liquids such as biological fluids.